Large diameter line pipe in the order of 36 to 64 inch diameters makes possible the transport of petroleum products, such as crude oil, from the oil fields to storage tanks or to the refineries in a highly efficient manner. The oil is pumped at high pressures through the pipeline continuously regardless of the weather or any other factors, overland or off shore, hundreds or thousands of miles, a feat which cannot be equalled by any other method.
The efficient forming of line pipe for many years has been a subject of research of some of the world's most talented mechanical engineers, metallurgists and physicists. Attempts have been made to successfully form large diameter line pipe from metal sheet or plate in a single operation, but insofar as can be determined, none has been successful. Today, the most widely used method of forming line pipe involves a complicated, fivestep process known as the UOE process. In the UOE process, giant presses are utilized to convert a plate of steel into the tubular article. After machining the edges of the plate, the edges are first crimped; secondly, the plate is formed into a U; thirdly, the article is formed into an O utilizing an extremely large press; fourth, the article is seam welded; and, fifth, the article is expanded from within in an effort to minimize the out-of-round imperfections.
The presently used process is highly capital intensive. The cost of a complete facility has kept many companies, and even entire countries, from making line pipe, although there is an ever increasing need for such production. Furthermore, these installations produce pipe sections that leave much to be desired in terms of the physical geometry of the pipe. The longitudinal areas adjacent to the edges of the steel plate that come together for butt seam welding, tend to have "flats" along the entire length of the pipe. The extra crimping heavy press operation is an attempt to remove part of this difficulty, but this has not been totally successful. Also, sections of the pipe spaced approximately 30.degree. to both sides of the seam tend to have detrimental compressive crystal dislocations adversely affecting the metal thickness. This is due to the extremely high tangential compressive stresses that are generated in the plate layers by the huge press brake machines in an endeavor to obtain sufficient radial forces to form the plate against the die inner wall which is circular.
Also, processes are known wherein metal sheet or plate is converted to a circular product utilizing a mandrel against which the blank is forced by cooperating rollers or other members. Such a process is shown, for example, in the prior U.S. Pat. No. 1,968,455, L. Jones, issued July 31, 1934. The use of a mandrel is inefficient because of the phenomena of "spring back" of the metal. In reality, the Jones' machine would be operative only with very malleable metals, and not with high strength metals necessary for modern day pipeline construction.